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I've been taking the original gravity and multiplying the apparent attenuation of the yeast. For instance:

1.040 OG x 75% apparent attenuation = 1.010 expected FG

But I never seem to get there. My fermentations look really healthy. Are my expectations realistic? Is this just hard to get right?

Here's a real world example:

I made a beer using this recipe:


  • 0.5 lb 40L Caramalt
  • 3.3 lbs extra-light LME
  • 1 lb extra-light DME

  • 1 oz Fuggle @ 60 mins

  • 1 oz Fuggle @ 1 min

  • 0.5 Whirlfloc tab @ 10 mins

  • 0.5 tsp Wyeast yeast nutrient @ 10 mins

Yeast: Wyeast 1098 British Ale

OG: 1.038

Very short lag, healthy-looking initial fermentation with a clean white foam cap that fell back into the beer after three days.


This yeast has an apparent attenuation range of 68-72%. Thus, I would expect an FG of 1.010 to 1.012.

When I put it in bottles last night, it came in at 1.016.

I appear to be doing everything recommended. For aeration, I'm pouring through a sieve, then sloshing for five minutes. Maybe that's the missing link? Or are my expectations too high?

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Out of curiosity, is 1.040 your actual OG, or predicted? –  hookedonwinter Feb 19 '10 at 17:01
    
Also, what is your FG when you're hoping for 1.010? –  hookedonwinter Feb 19 '10 at 17:03
    
Aerating like that is fine. –  Dean Brundage Feb 20 '10 at 14:42
    
And what does your hydrometer read when its sitting in 60F water? –  brewchez Feb 24 '10 at 13:23
    
As a post mortem to this, I had a few pints of the ale in question last night and it was great. Didn't taste underattenuated. –  Rich Armstrong Feb 26 '10 at 21:15
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3 Answers

up vote 3 down vote accepted

The yeast strains usually come with an apparent attenuation range, not an exact value. For instance, something like 70-75%, 67-70%, etc. I always hope to hit the lower end of that range. For example, if I start at 1.050 and use a yeast with 73-80% apparent attenuation, I expect to end up in the range of 1.010 - 1.014. Sometimes I go a point or two lower in FG than the high end of the attenuation range would suggest, but that's not the norm. If I get within a few gravity points of the higher gravity number, I'm happy.

If you're expecting to hit 1.010 and you're getting to, say, 1.022 something's wrong. Maybe you need to pitch more viable yeast. A starter might help. Or maybe your wort isn't aerated enough prior to fermentation.

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Your final gravity will be influenced by a number of things. The typical attenuation range of the yeast is just one aspect. How thick/thin and warm your mash is (or the overall fermentability of your LME or DME) will play a significant roll. Fermentation temperature and aeration of the wort before pitching will also be significant. As JackSmith stated, the amount and viability of the yeast will also influence final gravity. A solid yeast starter is highly recommended, especially with a stir plate.

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Unfortunately, not all extracts are created the same. I think what you are seeing is that your extract is not as fermentable as the extract created by say Wyeast to give you their range of attenuation. You can easily email Wyeast or WhiteLabs to ask them about the conditions used to get the attentuation ranges. The are generally very helpful with that sort of stuff.

I'd also check to see that when your hydrometer is sitting in water alone (preferably the same water used for your brewing) that its reading 1.000. Be sure you conduct that test at the calibrated temp for your hydrometer. Usually, 60F but it should be printed on the hydrometer scale somewhere.

So be sure your wort was at that temp too. It will only maybe throw off your reading a point or so, but it has an impact. The opposite is also true, be sure your OG was taken at 60F and not at 200F or even 100F.

I pose these hydrometer thoughts because I have a hard time getting 1.038 out of your recipe at 5 gallons. I get closer to 1.035-36. Small differences but it suggest some errors in reading or in the instrument itself.

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Thanks. Hydrometer had been calibrated against 60F water and comes out at 1.000. Readings were taken around 65F, not really enough to add a point. You're right that this recipe comes out about 1.035, but I think the initial question still applies. With an OG of 1.035, I should expect a FG of 1.008 or so. It still comes down to my not getting the attenuation I'm after. I used Northwestern Extract for this batch. –  Rich Armstrong Feb 25 '10 at 13:37
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